1. Field of the Invention
The present invention relates to a light semitransmitting type liquid crystal display device.
2. Description of the Related Art
In recent years, techniques relating to a reflective type liquid crystal display device without using a backlight have been developed, which are excellent at making a liquid crystal display device low-profile, lightweight and low-power-consumption.
There are two types of reflective type liquid crystal display devices: a function separation type wherein a light reflecting layer with a mirror surface is disposed on a surface of a rear placed substrate and a scattering plate is disposed outside a front placed substrate (Japanese Unexamined Patent Publication JP-A 8-201802 (1996)); and a scattering reflection type wherein an uneven light reflecting layer is formed on a rear placed substrate (Japanese Unexamined Patent Publication JP-A 4-243226 (1992)). Both the types do not use a backlight, thereby effectively using ambient light.
A scattering reflection type of TN-mode or STN-mode liquid crystal display device is shown in FIG. 19.
In FIG. 19, a liquid crystal display device 1 comprises a glass substrate 2, a group of bumps formed on the glass substrate 2 by arranging at random a lot of almost hemispherical bumps 3 made of resin in a photolithography process, a light reflecting layer 4 made of metal with which the group of bumps is coated, and an orientation layer 5 with which the light reflecting layer is coated. The liquid crystal display device further comprises a glass substrate 6, a color filter 7 formed on the glass substrate 6, an overcoat layer 8 with which the color filter is coated, a plurality of transparent strip electrodes 9 made of ITO or the like arranged on the overcoat layer 8, and an orientation layer 10 with which they are coated. Both the substrates are opposed to each other via liquid crystal 11 sealed into a region surrounded by a seal member 12, and a first retardation film 13, a second retardation film 14 and a polarizer plate 15 are sequentially formed on the outer surface of the glass substrate 6.
The light reflecting layer 4 is formed by coating the group of bumps with a metal film such as A1 film by spattering The A1 film is made of a lot of strips arranged in parallel, and the respective strips correspond to individual electrodes (the light reflecting layer 4).
In the liquid crystal display device 1 of the above construction, light enters sequentially the polarizer plate 15, the second retardation film 14, the glass substrate 6 and the liquid crystal 11, and is reflected by the light reflecting layer 4. The reflected light is emitted through the liquid crystal 11 again, and thus the device 1 is of scattering reflection type.
Other than such a reflective type liquid crystal display device, an STN light semitransmitting liquid crystal display device which can be used both outdoors and indoors has been developed for a portable information terminal and the like.
The light semitransmitting type liquid crystal display device is used as a reflective type device with an external lighting such as sunlight or a fluorescent lamp and used as a light transmitting type device with a backlight mounted as an internal lighting, and in order to have both the functions, the device has a light semitransmitting film (refer to Japanese Unexamined Patent Publication JP-A 8-292412 (1996)). In addition, it is proposed for like purposes to use a light semitransmitting film in an active matrix type of light semitransmitting type liquid crystal display device (refer to Japanese unexamined Patent Publication JP-A 7-318929 ( 1995)).
Also as such a light semitransmitting type liquid crystal display device, the one of function separation type is known, wherein a light semitransmitting film is disposed on a surface of a rear placed substrate and a light scattering plate is disposed outside a front placed substrate.
However, in a light semitransmitting type liquid crystal display device of function separation type as described above, a light scattering plate (a front scattering film or the like) is placed outside a front placed substrate, so that specifically in the case where the device is used as a reflective type device, there is a problem that when ambient light enters the device, the incident light scatters in the travelling direction thereof while light scattered by the light scattering plate is generated (backscattering).
Backscattering always occurs regardless of an on/off operation for each pixel, so that in the off state, the luminance of black becomes high due to the backscattering and the contrast is lowered.
Therefore, an object of the present invention is to provide a light semitransmitting type liquid crystal display device wherein it is avoided that the contrast is lowered due to backscattering in a reflective type display mode.
As shown in FIGS. 1 and 11, the invention provides a light semitransmitting type liquid crystal display device comprising a first substrate member including a first substrate, a group of bumps which is formed on one surface of the first substrate and composed of a lot of bumps which are made of a transparent resin and are arranged at random, a first group of light semitransmitting electrode stripes with which the group of bumps is coated and a first orientation layer formed on the first group of light semitransmitting electrode stripes; and a second substrate member including a second light transmitting substrate, a second group of transparent electrode stripes formed on the second light transmitting substrate and a second orientation layer formed on the second group of transparent electrode stripes, wherein the first group of light semitransmitting electrode stripes and the second group of transparent electrode stripes are bonded via nematic liquid crystal so as to intersect each other, to arrange pixels in a matrix form.
As shown in FIGS. 10, 12, 13 and 14, the invention provides another light semitransmitting type liquid crystal display device a first substrate member including a first substrate, a group of bumps which is formed on one surface of the first substrate and composed of a lot of bumps which are made of a transparent resin and are arranged at random, a light semitransmitting film with which the group of bumps is coated, a first group of transparent electrodes formed on the light semitransmitting film and a first orientation layer formed on the first group of transparent electrodes; and a second substrate member including a second light transmitting substrate, a second transparent electrode formed on the second light transmitting substrate and a second orientation layer formed on the second transparent electrode, wherein nematic type liquid crystal is interposed between the first substrate member and the second substrate member to arrange pixels in a matrix form.
As described above, according to the invention, a group of bumps composed of a lot of bumps which are made of transparent resin and are arranged at random is formed on a substrate and the group of bumps is coated with the group of light semitransmitting electrode stripes, or a group of bumps composed of a lot of bumps which are made of transparent resin and are arranged at random is formed on the substrate and the group of bumps is coated with a light semitransmitting film, so that a light scattering plate can be omitted. This solves a conventional problem of occurrence of backscattering and reduces the brightness in the off state in the reflective type display mode, with the result that it is possible to provide a high-performance light semitransmitting type liquid crystal display device with increased contrast.
In the light semitransmitting type liquid crystal display device of the invention it is preferable that the light semitransmitting film is made of one or more metals selected from the group consisting of Cr, Al and Ag, and has a thickness of 50 to 500 xc3x85.
In the light semitransmitting type liquid crystal display device of the invention, it is preferable that the light semitransmitting film has a reflective type index of 30 to 65% and a transmissivity of 15 to 50%.
In the light semitransmitting type liquid crystal display device of the invention, it is preferable that the semitransmtting film is composed of alternately laminated first-refractive-index layers 54 and second-refractive-index layers 55, which second refractive index is higher than the first refractive index.
In the light semitransmitting type liquid crystal display device it is preferable that the first-refractive-index layer 54 is made of one or more selected from the group consisting of SiO2, AlF3, CaF2 and MgF2 and has a thickness of 25 to 2000 xc3x85, and the second-refractive-index layer 55 is made of one or more selected from the group consisting of TiO2, ZrO2 and SnO2 and has a thickness of 25 to 2000 xc3x85.
In the light semitransmitting type liquid crystal display device of the invention, it is preferable that the light semitransmitting film has a thickness of 50 to 12000 xc3x85.
In the light semitransmitting type liquid crystal display device of the invention, it is preferable that the first-refractive-index layer 54 has a refractive index of 1.3 to 1.6 and the second-refractive-index layer 55 has a refractive index of 2.0 to 2.8.